Portion of a toothbrush



FIG. 1 is a front perspective view of the portion of the toothbrush according to one embodiment of the new design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a right side view, the left side being a mirror image thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a front view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken line showing of bristles is for the purpose of illustrating environmental structure that forms no part of the claimed design. 

The ornamental design for a portion of a toothbrush, as shown and described. 